The present invention relates to combine harvesters and has particular reference to such machines having rotary separating mechanisms.
In known combine harvesters, grain is threshed and separated in a threshing and separating mechanism and the separated grain, together with the impurities, such as chaff, dust, straw particles, and tailings, is fed to a cleaning mechanism for cleaning. Clean grain is collected below the cleaning mechanism and fed to a grain tank for temporary storage. The tailings are separated from the clean grain and impurities for reprocessing. This reprocessing either involves recycling the tailings through the threshing and separating mechanism or treating them in a separate tailings rethreshed means.
While the terms "grain", "straw", and "tailings" are used principally throughout this specification for convenience, it should be understood that these terms are not intended to be limiting. Thus "grain" refers to that part of the crop which is threshed and separated from the discardable part of the crop material which is referred to as "straw". Incompletely threshed ears are referred to as "tailings".
Recent developments in combine harvesters have lead to so called rotary machines wherein both threshing and separating are accomplished in mechanisms comprising rotary components cooperable with respective stationary threshing and separating concaves and grates. In conventional combine harvesters, grain separation is accomplished by straw walkers. In rotary combines the crop material is subjected to a much more aggressive and positive separating action during a relatively prolonged period of time, whereby the efficiency of a rotary combine harvester usually is greater than that of a conventional machine.
Several types of rotary combine harvester have appeared on the market and in one such machine a conventional transversely-extending, threshing mechanism having a threshing cylinder and a cooperable concave is combined with a rotary separating mechanism having a rotor of a width greater than that of the threshing mechanism and disposed parallel thereto with its ends extending transversely past the respective ends of the threshing mechanism. The rotary separating mechanism operates spirally to convey the crop material received from the threshing mechanism towards each of its ends, while submitting the crop to a separating action. With such a separating mechanism, the incoming layer of crop material has to be divided in two substantially equal portions, each of which is then spirally conveyed from the center of the separating mechanism to one or other of its ends.
The straw issuing from the ends of the separating mechanism is discharged from the machine through respective discharge channels which are called straw hoods, the straw being deflected downwardly at the ends of the straw hoods for final discharge to the ground either through respective discharge openings, or a single opening to which both streams of straw are directed to form a central windrow. In the case of other rotary machines, a single straw hood and discharge opening may be provided. The straw is propelled through the or each straw hood by the separating rotor but in certain circumstances, the straw may not be propelled far enough through the or each discharge channel, whereby it falls short thereof and is discharged onto the steerable wheels and/or the associated wheel axle of the machine which are normally located in the vicinity of the front edge of the or each discharge opening.
Discharge of straw in any relatively large quantity onto the steerable wheels and/or the associated wheel axle gives rise to two problems; the first is that the straw can be subjected to further breakage by the wheels and pressed against the ground surface in compacted form rather than in a fluffy windrow as is desired, and the second is that straw can bridge the or each wheel and/or associated wheel axle and build up to such an extent that the or each straw hood can be blocked. Such blockage or plugging of the machine can only be removed manually with consequential downtime of the machine and can also result in machine damage.